Gun perforator and explosive projectile therefor



Oct. 5, 1965 T. A. ANDREW 3,209,650

GUN PERFORATOR AND EXPLOSIVE PROJECTILE THEREFOR Original Filed Sept. 19, 1960 3 Sheets-Sheet 1 BY @wf Mirar/29s Oct. 5, 1965 T. A. ANDREW 3,209,650

GUN PERFORATOR AND EXPLOSIVE PROJEGTILE THEREFOR Original Filed Sept. 19, 1960 3 Sheets-Sheet 2 AA n v w i r 120 A 71E/@Mas ,4 ,4A/agay affito/72W Oct. 5, 1965 T. A. ANDREW 3,209,650

GUN PERFORATOR AND EXPLOSIVE PROJECTILE THEREFOR Original Filed Sept. 19, 1960 '3 Sheets-Sheet 3 IN VEN TOR. ZAM/.4.5 ,4l 4A/525W Jafar/2e .5

United States Patent O 3,209,650 GUN PERFORATUR AND EXPLOSIVE PROJECTILE THEREFGR Thomas A. Andrew, 222 Prospect St., Newport Beach, Calif. Continuation of application Ser. No. 56,919, Sept. 19, 1960. This application Apr. 30, 1963, Ser. No. 277,419 Claims. (Cl. 89-1) This application is a continuation of my copending apphcation Serial No. 56,919, tiled September 19, 1960, now abandoned, entitled Gun Perforator and Explosive Projectile-Therefor.

This invention deals generally with well equipment and particularly with improvements in so-called gun perforators.

Gun perforators for perforating well casings and/or the earth formation about a well bore are well known in the prior art and comprise, briey, a gun body which is lowered into a well bore by a cable or other suitable running-in string. The gun body embodies means for tiring a plurality of projectiles through the well casing into the surrounding earth formation to perforate the casing and formation and thereby promote drainage of tluid into the well bore.

The most efficient gun perforators are those that establish the most effective drainage channels into the oil bearing formation. It is well known to those acquainted with the art that the only present method of increasing eiciency in this regard is to penetrate the formation more deeply or to increase the diameter of the penetration. Either of these methods exposes more of the oil `bearing formation to permit a faster or more ellicient oil production process. In most cases, a steel liner or casing must be perforated ybefore the formation is contacted while in certain other cases, such as where the earth formation is oil bearing limestone, etc., the steel casing is not required so that the formation .may be entered immediately. In this regard, it is felt that the etliciency of the oil well formation penetration process would be greatly increased if the gun perforator projectiles were of a type that exploded after penetration of the formation to form large drainage pockets. These cavities, being the center of zones of fractured formation, would provide greatly increased areas of oil formation drainage to increase and make more efficient the oil production process.

A general object of this invention is to provide an irnproved gun perforator which tires explosive projectiles.

A more specific object of the invention is to provide a gun perforator of the character described in which detonation of the explosive charge in the projectiles is initiated by ignition of a fuse material in the projectile by the burning propellant gases which propel the projectile from the perforator gun and in which unique means are provided to delay ignition of the fuse material until the projectile has been propelled some distance through its barrel in the gun so as to attain maximum penetration of the projectile into the surrounding earth formation before detonation of the projectile.

Another object of the invention is to provide a gun perforator of the character described which can be equipped with any of the well-known means for restraining projectile move-ment until the burning propellant gases that propel the projectile from the gun develop the predetermined high pressure necessary to attain the high projectile velocities required for maximum penetration of the projectile into the surrounding earth formation.

A further object of the invention is to provide an explosive projectile for a gun perforator of the character described.

Yet a further object of the invention is to provide a gun perforator of the character described which is simple,

3,2%,659 Patented Oct. 5, 19.65

relatively inexpensive, and otherwise ideally suited to its intended purposes.

Other objects, advantages, and features of the invention will become readily apparent as the description proceeds.

Briey, these objects of the invention are attained by providing a gun perforator equipped, in the usual way, with a gun ybody which is adapted to be lowered into a well bore by means of a cable or other suitable running-in string. This gun body has a plurality of transversely extending, circumferentially and longitudinally spaced barrels to receive the projectiles to Ibe ltired. The barrels terminate at their inner ends in chambers to contain the propellent charges which propel the projectiles from the gun body. Various means are known to the prior art for confining the gases generated by the propellant charges after ignition thereof and restraining the projectiles against movement until the propellant gases develop the high pressure necessary to attain the high projectile velocities required for maximum penetration of the projectiles into the surrounding earth formation. Any one of these gas contining and projectile restraining means may be employed in the present gun perforator.

The actual improvements of the invention reside in a unique explosive projectile for use in the gun and a unique means for delaying explosion of the projectile until the latter has penetrated to a substantial depth in the earth formation surrounding the well bore. Briefly, the means for delaying explosion of the projectile comprise a fuse material in the projectile which is exposed through a rear opening in the projectile body for ignition by the burning propellant gases which propel the projectile from the gun body, and a flame propagation protective bore which receives the rear end of the projectile body containing the fuse ignition opening. v

The arrangement is such that the fuse material in the projectile is not exposed to the burning propellent gases until the rear end of the projectile is withdrawn from its ame propagation protective bore. This, of course, occurs only after the projectile has been propelled some distance through its barrel. After withdrawal of the rear end of the projectile from its flame propagation protective bore, the fuse material in the projectile is ignited and continues to burn during penetration of the projectile into the surrounding earth formation. This burning Ifuse material eventually ignites an igniter in the projectile which, in turn, detonates the main explosive charge in the projectile after the latter has reached the end of its trajectory in the formation.

In one `form of the invention, the fuse ignition opening is provided directly in the main body of the projectile. In a second form of the invention, the fuse ignition opening is in the rear end of a fuse tube which extends from the projectile body.

The engagement of the rear end of the projectile in its llame propagation protective bore provides an initial delay in the final detonation of the main explosive charge in the projectile which allows the burning propellent gases to reach the high pressure necessary to attain the required high projectile velocity. The time required for withdrawal of the rear end of the projectile from its flame propagation protective bore provides a second delay in the nal ignition of the explosive charge in the projectile during the which the latter travels some distance through its gun barrel and attains a high velocity. A iinal delay in the ignition of the main explosive charge in the projectile is furnished by the time required for the burning fuse material to proceed to the igniter and the time required for the latter to cause detonation of the main charge. Proper design of the llame propagation protective means and selection of a fuse material of the proper burning rate will assure sultcient delay for the projectile to penetrate the surrounding earth formation to an appreciable depth before explosion of the projectile.

The invention will now be described in greater detail by reference to the attached drawings, wherein:

FIG. 1 illustrates the present gun perforator in an operative position in a well bore;

FIG. 2 is an enlarged section through one projectile firing mechanism of the gun perforator shown in FIG. l showing the parts before tiring;

FIG. 3 is a view similar to FIG. 2 showing the parts after tiring;

FIG. 4 is a section taken along line 4-4 of FIG. 3;

FIG. 5 is a section through one barrel of a modified gun perforator according to the invention showing the parts before tiring;

FIG. 6 is a view similar to FIG. 5 showing the parts after firing;

FIG. 6a is a section through one barrel of another modified gun perforator according to the invention showing the parts before firing;

FIG. 7 is a section through one barrel of yet another gun perforator according to the invention showing the parts before tiring; and

FIG. 8 is a view similar to FIG. 7 showing the parts after ring.

Reference is first made to FIG. 7 of these drawings in which the numeral denotes a well bore in the earth. Extending into this well bore is a conventional well casing 22. The present gun perforator 24 is lowered into the casing 22, to a desired depth, by means of a cable 26 or other suitable running-in string.

Gun perforator 24 comprises a metal, cylindrical gun body 23 having a plurality of transversely extending barrels 30 spaced axially and circumferentially of the gun body. As will be presently more fully discussed, explosive projectiles of the present invention are red from the barrels 30 through liner 22 into the surrounding earth formation 32 and explode at the end of their trajectory in the formation to form a series of enlarged drainage pockets 34 which communicate with the interior of the well casing 22 through passages 38 formed by the projectile.

Reference is now made to FIGS. 2 and 3 which illustrate one barrel of the gun body 28 in FIG. l. As shown in these latter gures, the barrel 3i) comprises a hardened metal insert which is threaded into the gun body 28 and has a bore 4t) which receives a projectile 42 of the present invention. The rear end of the bore 4t) opens to a chamber 44 which contains the propellent charge 46 for propelling the projectile 42 from its bore 40. This charge is ignited in any suitable manner through an ignition hole 48 in the gun body 28. Propellent charge 46 is contained between plastic end caps Si? which serve as containers for the propellant during forming, storage, and loading procedures. Seals 52 and 54 are provided for preventing leakage of gas from the chamber 44 past the gun barrel 30 as well as leakage of uid in the well bore into the propellent chamber. In some cases, the bore 40 in the gun barrel may be sealed by a rubber plug 56 against which the hydrostatic pressure of the Huid in the well casing 22 acts. The inner end of this plug is shaped to receive the nose of the projectile 42 and is tightly wedged against the wall of the bore 4t), to effectively seal the latter against leakage of well fluid into the propellent chamber, by the action of hydrostatic pressure forcing the plug between the nose of the projectile and the wall of the bore 40.

In the form of the invention illustrated in FIGS. 2 and 3, the explosive charge 46 and its end caps 5t) are formed with central bores or holes through which the body of the projectile 42 extends. The rear end of the projectile body has a close iit within a flame propagation protective bore 5S in the rear wall of the propellant chamber 44.

The nose 42a and the body 42!) of the projectile are made in separate pieces which intertit, as shown, and are rigidly joined in any suitable manner. Formed in the rear face of the projectile nose 42a is a chamber 6) containing an igniter 62. Extending longitudinally through the body 42b of the projectile and opening at their forward ends into the igniter chamber 6i) are a series of bores or chambers 64 containing a suitable high power explosive charge 66. The several chamber 64 are circumferentially spaced about the axis of the projectile, as may be best observed in FIG. 4. Extending axially through the body 42h of the projectile is a small bore or hole 68 containing a relatively slow burning fuse material 70. The forward end of the fuse hole 68 opens to the igniter chamber 60. The rear end of the fuse hole 68 opens through the rear face 72 of the projectile body 42h to form a fuse ignition opening.

In the form of the invention under discussion and in a later form of the invention shown in FIGS. 7 and 8, a small clearance space, indicated at 73 in FIGS. 2 and 3, is provided between the periphery of the projectile and the wall of its gun bore 40. This establishes a gas flow path between the propellant chamber 44 and the gun bore 4t) in advance of the projectile. As noted earlier, however, the projectile body 4211 has a relatively close t in the flame propagation protective bore S8 which restricts the flow of gases from the propellant chamber to the rear ofthe projectile.

As a consequence, the gases created by the propellent `charge 46 following the ignition thereof through the ignition hole 48 are initially confined to a major degree in the propellant chamber so that the .pressure in the chamber rises quite rapidly. yOn the other hand, the restricted flow of gases from the propellant chamber to the rear of the projectile results in a relatively slow development of the pressure acting on the rear of the projectile and tending to propel the later from the gun. Accordingly, an interval o-f time (actually of exceedingly short duration) expires before the gas pressure .acting on the rear of the projectile `develops sufficiently to propel the latter through the bore 40. During this interval of time, some gas under pressure passes through the clearance space 73 between the projectile 42 and the wall of its gun bore 40 into the gun bore ahead of the projectile. This pressure in the gun bore tends to hold the projectile rearwardly against the gun body .and thereby retain the rear end of the projectile in its flame propagation protective *bore 58. Also, the gas pressure in the gun bore ahead of the projectile exerts a force on the sealing plug 56 tending to expel the latter from the gun bore. Eventually, this gas pressure force equals and then exceeds the hydrostatic head of the well Huid acting on the outer end of the plug and tending to hold the latter in the gun bore. When this Occurs, the gas pressure in the gun bore behind the plug blows the latter and well uid out of the gun bore to clear the latter for subsequent movement of the projectile therethrough.

As just noted, the gas pressure in the propellant chamber is developing to a high value and the gas pressure acting on the rear face of the projectile is developing to a value sufficient to commence propulsion of the projectile 42 forwardly through` the gun bore during the interval of time under discussion.

Subsequent forward movement of the projectile through the .gun bore, of course, results in withdrawal of the rear end of the projectile body from the ame propagation protective bore 58. Immediately upon withdrawal of the end of the projectile from the bore 58, the high gas pressure then existing in the propellant chamber becomes effective to propel the projectile from the gun at an exceedingly high velocity.

The clearance between the outer surface of the projectile body 42b and the wall of the ame propagation protective bore S8 is made large enough to permit gas leakage from the propellant chamber 44 to the rear of the projectile fit-ting in the bore, as discussed above, but sufficiently small to prevent flame propagation from the burning gases in the propellant chamber to the rear of the projectile. While the rear end of the projectile is wi-thin the flame propagation protective bore, therefore, the rear, open end of the fuse hole 68 on the projectile is shielded `against the flame of the burning propellent gases and the fuse material in the hole is not ignited.

Upon withdrawal of the rear end of the pr-ojectile `from the flame Apropagation protective bore during forward movement of the projectile through the barrel bore 40, the fuse material in the fuse ignition opening at the rear end of the fuse hole 63 is exposed to and ignited by the flame in the propellant chamber 44. The fuse material then continues to burn forwardly through the fuse hole 68 and toward the main explosive igniter 62 in the projectile during travel of the projectile from the lgun bore 40, through the well casing 22, into the surrounding earth formation 32. The fuse material is selected to have a burning rate tht will all-ow the projectile to reach the end of its trajectory in the earth formation before ignition of the projectile explosive igniter 62. Ignition of the igniter by the fuse material creates sufiicient heat and pressure to detonate the main explosive charges 66 in the projectile.

Detonation of the main explosive charges in the projectile explodes the lat-ter to produce a drainage pocket 34 in the earth formation, as already mentioned. As noted in the discussion of FIG. l, the gun body 28 is provided with several longitudinal-ly and circumferentially spaced barrels identical to that just described from which several explosive projectiles 42 are fired through the well casing 22 into the surrounding earth formation 32 to form a number of drainage pockets 34 for inducing How of uid from the formation to the interior of the Well casing. This uid is later pumped from the well casing to the surface. Explosion of the projectiles also fractures the earth formation about each drainage pocket and the fragments of the projectiles penetrate the formation about each pocket to produce a myriad of fissures leading to each pocket which pro-mote flow of liquid from the formation to the pockets.

FIGS. 5 and 6 illustrate a modified `gun perforator o-f the invention having an alternative prior art means to contain the propellent gases in the gun and res-train the projectile against movement until the gas pressure in the propellant chamber ldevelops to the high value necessary to produce the high projectile velocity required for proper penetration of the projectile into the surr-ounding earth formation. These figures also illustrate :an alternative means for delaying ignition of the fuse material in the projectile until the pressure in the propellant chamber becomes sufi'icient to propel the projectile from the gun. The gun perforator of these latter figures comprises, as before, a gun body 28 having a plurality of longitudinally and circumferentiaflly spaced barrel inserts 30 (only one shown). Barrel 30 has a bore 40 which receives a modified projectile 100 and a propellant chamber 44 at the rear end of the bore 40. This chamber contains the propellent charge 102 which propels the projectile 100 from the gun body.

The propellent charge 102 is substantially identical to the propellent charge in the p-revious form of the invention and includes end caps 104 which serve as containers for the Ipropellant during forming, storage, and loading procedures. As in the previous form of the invention, gases are prevented from escaping from the propellant chamber 44 past the outside of the barrel 30, and fluid in the well bore is prevented `from seeping into the propellant chamber past the outside of the barrel, by seal rings 52 and 54. In FIGS. 5 and 6, fluid in the well bore is prevented from entering the gun bore 40 by a sealing disc 105 4fitted in a counterbore 106 at the outer end of the barrel. If desired, of course, the bore 40 could be further sealed by a rubber plug, as in the first form of the invention.

The modified project-ile 100 comprises a cylindrical body 100:1 and a separate nose 100b which are joined in any suitable way and contain, as before, a chamber 108 containing an igniter 110, generally longitudinal bores or chambers 112 which open at their forward ends to the igniter chamber 103 and contain the main explosive charges 114 in the projectile, and a fuse hole 116 which extends axially through the projectile body g and opens at its forward end to the explosive igniter chamber 108.

Thus far, therefore, the projectile 100 is identical to the projectile of the first form of the invention. The projectile 100 differs from the earlier projectile in that the rear end of the fuse hole 116 is counterbored at 118 and in this counterbore is tightly fitted a fuse tube 120 which, in effect, forms the rear end of the projectile. The fuse tube has an axial hole 122 which, and the fuse hole 116 in the main projectile body 100g, contains the slow burning fuse material 124. As shown, the forward eud of the fuse hole 122 in the fuse tube 120 opens to the fuse hole 116 in the main projectile body and the rear end of the fuse hole 122 opens through the rear end of the fuse tube 120 to form a fuse ignition opening.

The forward end of the propellant chamber 44 in the gun perforator of FIGS. 5 and 6 is elosed off from the bore 40 by a shear disc 126. This shear disc is located within a space which is provided in the modified casing perforating gun between the right-hand end cap 104 on the propellent charge 102 and the left-hand end face of the barrel 30. The shear disc, the propellent charge 102, and the end caps 104 thereon have coaxial holes 105' through which the fuse tube 120 of the projectile loosely extends. The rear end of the fuse tube 120 projects rearwardly of the rear end cap 104 on the propellent charge into a fiame propagation protective bore 12S. When the projectile is properly inserted into the gun, the rear end face of the projectile body 108 seats against the front side of the shear disc 126. The rear end of the fuse tube 120 has a close lit in the flame propagation protective bore 128 which prevents the propagation of flame from the propellant chamber 44 to the ignition opening in the rear end of the fuse tube 120 when the latter is positioned in the bore.

When the propellent charge 102 is ignited through the ignition hole 4S in the gun body 28, the gases generated are initially confined in the propellant chamber by the shear disc 126. The pressure in the chamber, therefore, rises rapidly. Propagation of flame from the propellant chamber to the rear ignition opening of the fuse tube 120 of the projectile is prevented by the close fit of the tube in its flame propagation protective bore 128.

Eventually, pressure in the propellant chamber 44 becomes sufcient to rupture the shear disc 126. The high gas pressure in the propellant chamber then acts on the rear face of the projectile body 100ml and propels the projectile at a high velocity through the bore 40. During this travel of the projectile through the bore, the rear end of the fuse tube 120 is withdrawn from the iiame propagation protective bore 128. The fuse material 124 within the fuse tube, however, is not ignited until the ignition opening in the rear end of the tube is exposed to the flame in the propellant chamber 44 upon complete withdrawal of the tube from the bore 128. By this time, the projectile 100 has been propelled some distance through the bore 40 and has attained a high velocity. The fuse material continues to burn forwardly through the fuse tube and the fuse hole in the projectile body 100a toward the projectile explosive igniter 110, during travel of the projectile from the bore 40, through the well casing 22, into the surrounding earth formation 32. The fuse tube 120 is provided with such a length and the fuse material is selected to have a suiciently slow burning rate as to permit the projectile to reach the end of its trajectory in the earth formation before the igniter 108 is ignited by the burning fuse material to cause detonation of the main explosive charges 112 in the projectile.

As before, detonation of these charges explodes the projectile to produce a drainage pocket in the earth formation.

FIG. 6a illustrates another shear disc arrangement in which the projectile h' extends through a hole 195 in the shear disc 126 and part way through the propellent charge 102. The portion of the shear disc about the hole 105 engages in an annular groove 126a in the projectile body. The shear disc 126', therefore, is, in effect, keyed to the projectile and restrains the latter against movement until the pressure of the gas generated by the propellent charge 102', after ignition thereof, develops to the high value required to rupture the disc. The remainder of the gun perforator and projectile of FIG. 6a is identical with that of FIGS. 5 and 6 so that no further discussion of the gun of FIG. 6a is deemed necessary.

FIGS. 7 and 8 illustrate a modification of the invention which is actually a combination of the casing perforating gun arrangements of FIGS. 2 and 5. Thus, the gun of FIGS. 7 and 8 comprises a gun body 28, barrel 30 havingy a bore 4i), a propellant chamber 44 and a propellent charge 46 which are identical to the corresponding parts of the casing perforating gun of FIG. 2, and a projectile 100 which is identical to the projectile of FIG. 5. The projectile has a loose t in the rear end of the bore 40, as noted earlier. A rubber plug 56 in the bore effectively seals the latter against the leakage of well duid to the propellant chamber. The body of the projectile extends through the center of the propellent charge 46 and its end caps 50 and the rear end of the projectile lits closely in the bore 58 which opens into the propellant chamber 44, all in the manner described in connection with FIG. 2. The fuse tube 120 of the projectile ts closely in a flame propagation protective bore 128 which opens, at its forward end, into the bore 53.

When the propellent charge 46 is ignited through the ignition hole 4S in the gun body, the gases generated by the burning propellant are initially confined to a major degree in the propellant chamber, as before, so that the pressure in the chamber rises rapidly, as described earlier. Some gas does flow to the gun bore 40, in advance of the projectile, and forces the plug S6 and well fluid from the bore, as described earlier. Because of the close lit of the rear end of the projectile in bore 58, there is a restricted How of gas from the propellant chamber to the rear of the projectile7 with the result that when the pressure acting on the rear end of the projectile becomes sufficient to propel the latter through the bore 46, the pressure in the propellant chamber 44 will have developed to a high value. Upon withdrawal of the rear end of the projectile from bore 58, this high pressure acts on the projectile to propel the latter at a high velocity from the gun.

The fuse material 124 within the projectile is not ignited until the rear end of the fuse tube is withdrawn from its flame protective bore 128 to expose the fuse ignition opening in the end of the tube to the ame in the propellant chamber, as described in connection with FIGS. 5 and 6. As before, the fuse material continues to burn forwardly through the fuse tube and the body of the projectile to the projectile explosive igniter 110 during travel of the projectile to the end of its trajectory. Ignition of the igniter by the burning fuse material, then, detonates the main explosive charges 112 in the projectile, exploding the latter to form a drainage pocket 34 in the surrounding earth formation.

In each form of the invention, therefore, an initial delay in the ignition of the fuse material in the projectile is attained by the close t of the rear end of the projectile in its flame propagation protective bore during which the gases in the propellant chamber are confined to a large degree and the pressure in the chamber rises rapidly to a high value necessary to attain the high projectile velocity required for proper penetration of the projectile into the surrounding earth formation. The time required for withdrawal of the rear end of the projectile, which, in the case f FIGS. 5 and 7, is the fuse tube 120, from the fiame propagation protective bore, to a position where the fuse ignition opening in the rear end of the projectile is exposed to the flame in the propellant chamber, provides a second delay in the ignition of the fuse material in the projectile during which the latter travels a distance through its barrel bore. A final delay in the detonation of the main explosive charge in the projectile is derived from the time required for burning of the fuse material in the projectile to proceed to the projectile igniter and the latter to detonate the main explosive charge in the projectile. The resultant total delay between initial ignition of the fuse material and final detonation of the main explosive charge in the .projectile is sufficient to enable the latter to reach the end of its trajectory before its explosion to form a drainage pocket.

From the foregoing description, it will be seen that the explosive train of the projectile has three basic parts, namely, a fuse material, an explosive igniter or detonator, and the main explosive charge. The function of the fuse material, of course, is to develop an appreciable delay during its burning period and, at the end of burning, to successfully ignite the igniter which may be described generally as the primary explosive in the system. This primary explosion detonates the secondary high explosive or main explosive charge in the projectile.

Various materials may, of course, be used for these parts of the explosive train. By way of example, acceptable items for fuse material are gun powders of the propellant type, such as smokeless powder (nitro cotton); black power (potassium nitrate, sulphur, charcoal) and DNT (di-nitro toluene ingredient); or lead spitter.

Suitable items for the primary high explosive, or igniter, are materials which are easily ignited and after ignition burn at such an extremely high rate that the end reaction is a detonation. Lead azide and lead styphnate are materials of this type.

The secondary high explosive or main explosive charge in the train is a material which requires a detonation wave for ignition and possesses the required brisance or shattering action. Suitable secondary high explosives for the present application are RDX (cyclo-trimethyl-enetrinitramine), Torpex (RDX-j-TNT-j-aluminum), HEX (RDX-j-TNT-j-aluminum-j-wax) or Pentolite (PETN-HNT) or PETN (pentaerythritol tetranitrate) or TNT (trinitrotoluene).

Clearly, therefore, the invention herein described and illustrated is fully capable of attaining the several objects and advantages set forth.

While the invention has been disclosed in connection with certain conventional projectile restraining means, it is equally capable of use with other conventional projectile restraining means and, therefore, the invention should not be thought of as limited in use with the restraining means disclosed herein. Numerous other modifications are, of course, also possible within the spirit and scope of the following claims.

I claim:

1. A gun perforator comprising: a gun body having a propellant chamber with a front wall and an opposite rear wall, a gun bore opening at its rear end through said front wall and at its forward end to the exterior of said gun body, and a flame propagation protective bore in said rear wall on the axis of said gun bore; a projectile including a cylindrical body and a slender fuse tube extending rearwardly from said projectile body along the central axis of the latter body, the forward end of said projectile body being positioned in said gun bore in advance of said chamber and said fuse tube extending into said protective bore; said projectile having a chamber in said projectile body and a passage extending through said fuse tube and opening at its forward end to vstantially greater than' the external diameter of said fuse tube and said projectile body having a rear annular face of substantial area surrounding said fuse tube on which the pressure of said propellant gas is adapted to act to propel said projectile forwardly through said gun bore; said fuse tube having a close sliding fit in said protective bore such that the annular clearance between the wall of said protective bore and the external surface of said fuse tube is sufficiently small to prevent the propagation of flame from said propellant chamber to said rear fuse ignition opening in said fuse tube when said fuse tube is positioned in said protective bore; and said fuse tube extending into said protective bore a distance which is many times the external diameter of said tube, whereby said fuse tube is withdrawn from said protective bore to expose said fuse ignition opening to flame in said propellant chamber only after said projectile has been propelled a substantial distance forwardly through said gun bore.

2. A gun perforator comprising: a gun body having a propellant chamber with a front wall and an opposite rear wall, a gun bore opening at its rear end through said front wall and at its forward end to the exterior of said gun body, and a flame propagation protective bore in said rear wall on the axis of said gun bore; a shear disc within said propellant chamber seating against and sealed to said front wall and extending across the rear end of said gun bore; a projectile including a cylindrical body and a slender fuse tube extending rearwardly from said projectile body along the central axis of the latter body; said projectile body being positioned in said gun bore in advance of said shear disc and said fuse tube extending through a close fitting hole in said shear disc and into said protective bore; said projectile having a chamber in said projectile body and a passage extending through said fuse tube and opening at its forward end to said projectile chamber and at its rear end to the exterior of the projectile through a fuse ignition opening in the rear end of said fuse tube; said passage containing a fuse material and said projectile chamber containing an explosive charge and an igniter for said explosive charge; a propellent charge in `said propellant chamber; means for igniting said propellent charge, thereby to create a pressurized propellant gas in said propellant chamber; the diameter of said projectile body being substantially greater than the external diameter of said fuse tube and said projectile body having a rear annular face of substantial area surrounding said fuse tube on which the pressure of said propellant gas is adapted to act to propel said projectile forwardly through said gun bore; said shear disc being adapted to confine said propellant gas within said propellant chamber until the pressure of said propellant gas becomes suilicient to rupture said disc, whereupon said projectile is propelled forwardly through said gun bore by said propellant gas; said fuse tube having a close sliding lit in said protective bore such that the annular clearance between the wall of said protective bore and the external surface of said fuse tube is sufficiently small to prevent the propagation of flame from said propellant chamber to said rear fuse ignition opening in said fuse tube when said fuse tube is positioned in said protective bore; and said fuse tube extending into said protective bore a distance which is many times the external diameter of said tube, whereby said fuse tube is withdrawn from said protective bore to expose said fuse ignition opening to flame in said propellant chamber only after said pro- 10 jectile has been propelled a substantial distance forwardly through said gun bore.

3. A gun perforator comprising: a gun body having a propellant chamber with a front wall and an opposite rear wall, a gun bore opening at its rear end through said front wall and at its forward end to the exterior of said gun body, and a second bore in said rear wall on the axis of said gun bore including a flame propagation protective bore and an enlarged counterbore at the end of said flame propagation protective bore adjacent said propellant chamber; a projectile including a cylindrical body and a slender fuse tube extending rearwardly from said projectile body along the central axis of the latter body, the forward end of said projectile body being positioned in said gun bore in advance of said propellant chamber, the rear end of said projectile body being positioned in said counterbore, and said fuse tube extending into said protective bore; said projectile having a chamber and said fuse tube having a passage opening at its forward end to said projectile chamber and at its rear end to the exterior of the projectile through a fuse ignition opening in the rear end of said fuse tube; said passa-ge containing a fuse material and said projectile chamber containing an explosive charge and an igniter for said explosive charge; a propellent charge in said propellant chamber; means for igniting said propellent charge, thereby to create a pressurized propellant gas in said propellant chamber; the diameter of said projectile body being substantially greater than the external diameter of said fuse tube and said projectile body having a rear annular face of substantial area surrounding said fuse tube on which the pressure of said propellant gas is adapted to act to propel said projectile forwardly through said gun bore; said counterbore receiving the rear end of said projectile body with a close sliding t such that the annular clearance space between the wall of said counterbore and the external surface of said projectile body restricts flow of said propellant gas to the rear of said projectile body to permit the pressure of said propellant gas to rise to a high value before said projectile is propelled forwardly through said gun bore by the pressure of said propellant gas; said protective bore receiving said fuse tube with a close sliding fit such that the annular clearance between the wall of said protective bore and the external surface of said fuse tube is sufliciently small to prevent the propagation 'of flame from said propellant chamber to said rear fuse ignition opening in said fuse tube when said fuse tube is positioned in said protective bore; and said fuse tube extending into said protective bore a distance which is many times the external diameter of said tube, whereby said fuse tube is withdrawn from said protective bore to expose said fuse ignition opening to flame in said propellant chamber only after said projectile has been propelled a substantial distance forwardly through said gun bore.

4. A gun perforator comprising: a gun body having a propellant chamber with a front wall and an opposite rear wall, a gun bore opening at its rear end through said front wall and at its forward end to the exterior of said gun body, and a flame propagation protective bore in said rear wall on the axis of said gun bore; a projectile including a cylindrical body and a slender fuse tube extending rearwardly from said projectile body along the central axis of the latter body, the forward end of said projectile body being positioned in said gun bore in advance of said propellant chamber and said fuse tube extending into said protective bore; said projectile body having a chamber and said fuse tube having a passage opening at its forward end to said projectile chamber and at its rear end to the exterior of the projectile through a fuse ignition opening in the rear end of said fuse tube; said passage containing a fuse material and said projectile chamber containing an explosive charge and an igniter for said explosive charge; a propellent charge in said propellant chamber; means for igniting said propellent charge, thereby to create a pressurized propellant gas in Said propellant chamber; the diameter of said projectile body being substantially greater than the external diameter of said fuse tube and said projectile body having a rear annular face of substantial area surrounding said fuse tube on which the pressure of said propellant Vgas is adapted to act to propel said projectile forwardly through said gun bore; a shear ring surrounding and engaging in an external groove in said projectile body and seating against the front wall of said propellant chamber to restrain said projectile against forward movement through said gun bore until the pressure of said propellant gas increases sufciently to shear said ring; said protective bore receiving said fuse tube with a close sliding t such that the annular clearance between the wall of said protective bore and the external surface of said fuse tube is sutciently small to prevent the propagation of flame from said propellant chamber to said rear fuse ignition opening in said fuse tube when said fuse tube is positioned in said protective bore; and said fuse tube extending into said protective bore a distance which is many times the external diameter of said tube, whereby said fuse tube is withdrawn from said protective bore to expose said fuse ignition opening to llame in Said propellant chamber only after said projectile has been propelled a substantial distance forwardly through said gun bore.

5. A gun perforator comprising: a gun body having a propellant chamber with a front wall and an opposite rear wall, a gun bore opening at its rear end through said front wall and at its forward end to the exterior of said ygun body, and a llame propagation protective bore in said rear wall on the axis of said gun bore; a projectile including a cylindrical body and a slender fuse tube extending rearwardly from said projectile body along the central axis of the latter body, the forward end of said projectile body being positioned in said gun bore in advance of said propellant chamber and said fuse tube extending into said protective bore; said projectile having a Chamber on the central axis of the projectile body and a multiplicity of generally longitudinal bores radially spaced from and circumferentially spaced about the central axis of the projectile body and opening at their forward ends to said projectile chamber, and said fuse tube having a passage opening at its forward end to said projectile CFI chamber and at its rear end to the exterior of the projectile through a fuse ignition opening in the rear end of said fuse tube; a fuse material in said passage, explosive charges in said projectile bores, respectively, and an igniter for said explosive charges in said projectile chamber; a propellent charge in said propellant chamber; means for igniting said propellent charge, thereby to create a pressurized propellant gas in said propellant chamber; the diameter of said projectile body being substantially greater than the external diameter of said fuse tube and said projectile body having a rear annular face of substantial area surrounding said fuse tube on which the pressure of said propellant gas is adapted to act to propel said projectile forwardly through said gun bore; said protective bore receiving said fuse tube with a close sliding fit such that the annular clearance between the wall of said protective bore and the wall of said fuse tube is suiliciently small to prevent the propagation of flame from said propellant chamber to said rear fuse ignition opening in said fuse tube when said fuse tube is positioned in said protective bore; and said fuse tube extending into said protective bore a distance which is many times the external diameter of said tube, whereby said fuse tube is withdrawn from said protective bore to expose said fuse ignition opening to flame in said propellant chamber only after said projectile has been propelled a substantial distance forwardly through said gun bore.

References Cited by the Examiner UNITED STATES PATENTS 2,292,670 8/42 Smith 89-1 2,345,619 4/44 Moore l02-92.5 2,376,227 5/45 Brown lO2-7.2 X 2,408,419 10/46 Foster 89-1 2,535,309 12/50 Mari IGZ-34.4 2,592,434 4/52 Krasnow l02-92.5 2,649,736 S/53 Phillips 89-1 2,773,424 12/56 Andrew 89-1 2,843,041 7/58 Stewart 89-1 3,056,351 10/62 Bares IGZ- 34.4

BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL W. ENGLE, Examiner. 

1. A GUN PERFORATOR COMPRISING: A GUN BODY HAVING A PROPELLANT CHAMBER WITH A FRONT WALL AND AN OPPOSITE REAR WALL, A GUN BORE OPENING AT ITS REAR END THROUGH SAID FRONT WALL AND AT ITS FORWARD END TO THE EXTERIOR OF SAID GUN BODY, AND A FLANGE PROPAGATION PROTECTIVE BORE IN SAID REAR WALL ON THE AXIS OF SAID GUN BORE; A PROJECTILE INCLUDING A CYLINDRICAL BODY AND A SLENDER FUSE TUBE EXTENDING REARWARDLY FROM SAID PROJECTILE BODY ALONG THE CENTRAL AXIS OF THE LATTER BODY, THE FORWARD END OF SAID PROJECTILE BODY BEING POSITIONED IN SAID GUN BORE IN ADVANCE OF SAID CHAMBER AND SAID FUSE TUBE EXTENDING INTO SAID PROTECTIVE BORE; SAID PROJECTILE HAVING A CHAMBER IN SAID PROJECTILE BODY AND A PASSAGE EXTENDING THROUGH SAID FUSE TUBE AND OPENING AT ITS FORWARD END TO SAID PROJECTILE CHAMBER AND AT ITS REAR END TO THE EXTERIOR OF THE PROJECTILE THROUGH A FUSE IGNITION OPENING IN THE REAR END OF SAID FUSE TUBE; SAID PASSAGE CONTAINING A FUSE MATERIAL AND SAID PROJECTILE CHAMBER CONTAINING AN EXPLOSIVE CHARGE AND AN IGNITER FOR SAID EXPLOSIVE CHARGE; A PROPELLENT CHARGE IN SAID PROPELLANT CHAMBER; MEANS FOR IGNITING SAID PRPELLENT CHARGE, THEREBY TO CREATE A PRESSURIZED PROPELLANT GAS IN SAID PROPELLANT CHAMBER; THE DIAMETER OF SAID PROJECTILE BODY BEING SUBSTANTIALLY GREATER THAN THE EXTERNAL DIAMETER OF SIAD FUSE TUBE AND SAID PROJECTILE BODY HAVING A REAR ANNULAR FACE OF SUBSTANTIAL AREA SURROUNDING SAID FUSE TUBE ON WHICH THE PRESSURE OF SAID PROPELLANT GAS IS ADAPTED TO ACT TO PROPEL SAID PROJECTILE FORWARDLY THROUGH SAID GUN BORE; SAID FUSE TUBE HAVING A CLOSE SLIDING FIT IN SAID PROTECTIVE BORE SUCH THAT THE ANNULAR CLEARANCE BETWEEN THE WALL OF SAID PROTECTIVE BORE AND THE EXTERNAL SURFACE OF SAID FUSE TUBE IS SUFFICIENTLY SMALL TO PREVENT THE PROPAGATION OF FLAME FROM SAID PROPELLANT CHAMBER TO SAID REAR FUSE IGNITION OPENING IN SAID FUSE TUBE WHEN SAID FUSE TUBE IS POSITIONED IN SAID PROTECTIVE BORE; AND SAID FUSE TUBE EXTENDING INTO SAID PROTECTIVE BORE A DISTANCE WHICH IS MANY TIMES THE EXTERNAL DIAMETER OF SAID TUBE, WHEREBY SAID FUSE TUBE IS WITHDRAWN FROM SAID PROTECTIVE BORE TO EXPOSE SAID FUSE IGNITION OPENING TO FLAME IN SAID PROPELLANT CHAMBER ONLY AFTER SAID PROJECTILE HAS BEEN PROPELLED A SUBSTANTIAL DISTANCE FORWARDLY THROUGH SAID GUN BORE. 